In a conventional magnetic recording disk drive used in the computer data processing environment the data is stored on the disks in fixed length (fixed number of bytes) physical sectors in a format called fixed block architecture (FBA). In a FBA disk drive, the concentric data tracks on the disks have a common index, which represents the start of the tracks, and each sector on each track has a physical sector number or address. Current disk drives in the computer data processing environment are characterized by random access patterns and small blocks of data. In contrast, in the AV environment the data processing is characterized by streams of large sequential blocks of data, and by the interleaving of multiple streams. For example, AV data stream interleaving allows a digital video recorder (DVR) to record and play back real-time television and to record two television programs simultaneously.
The benchmark for data storage in the AV environment is based on cost per unit of performance. The AV disk drive data workload is categorized by a dominance of large reads and writes, interspersed with small reads and writes that may post frequently but contain only small amounts of data. A disk drive, therefore, may find itself spending a significant time waiting due to rotational latency, i.e., the time delay required for the write head to wait for the disk to rotate until the index is detected before the next write can occur.
Another aspect of the AV environment is that if there is an uncorrectable error in a data sector on the disk, there is no time to re-read the data. Instead, the DVR will note that the data is incorrect, and attempt to conceal the missing bytes, such as by freezing the AV stream briefly to mask the error.
What is needed is an AV-optimized disk drive that does not suffer from delays caused by rotational latency and re-reading the data in the event of a data error.